This application is submitted in response to RFA AA-94-08 for renewal of support for the Pittsburgh Adolescent Alcohol Research Center (PAARC), located within the Department of Psychiatry of the University of Pittsburgh School of Medicine. PAARC is the only alcohol research center supported by the National Institute on Alcohol Abuse and Alcoholism that focuses on diagnosed alcohol abuse and dependence among adolescents aged 12 through 18 hears of age. The overarching goal of the Pittsburgh Adolescent Alcohol Research Center is to enhance understanding of the structure, development, and consequences of adolescent alcohol use disorders through cross-sectional and longitudinal investigations of clinical and community samples of adolescents (N=500). Specific goals of the projects for the next 5-year period are to: (1) Develop a new and more appropriate adolescent taxonomy of alcohol use disorders/ (2) Determine the impact of alcohol use disorders on the developmental transitions during adolescence and young adulthood; (3) Elucidate brain-behavior covariation among impulsive/aggressive alcohol abusing or dependent adolescents; (4) Clarify the psychobiological mechanisms pertaining to stress and trauma that may underlie the linkage between PTSD and adolescent alcohol use disorders; and, (5) Identify the precipitants of lapse and relapse in adolescents. Excessive alcohol consumption and its consequences comprise a prevalent and serious public health problem among American adolescents. our finding thus far reflect far greater clinical heterogeneity and severity than has been commonly assumed in this population. Furthermore, and most importantly, the biomedical and psychosocial findings from our comprehensive database emphasize that adolescents exhibiting alcohol use disorders cannot be assumed to be merely younger versions of adult alcoholics. The enhancement of understanding of the particular nature of alcohol problems in adolescence is a necessary prerequisite to the development of effective prevention and treatment methodologies for this population.